A. Related Applications
There are no applications related hereto heretofore filed in this or any foreign country.
B. Field of Invention
This invention relates to tools for reforming damaged threads in a blind hole and more particularly to such a tool having a first fluted end that may be inserted past the damaged threads and expanded to repair those threads upon withdrawal.
C. Background and Description of Prior Art
Threaded blind holes are common in machinery and mechanical apparatus, such as spark plug holes in an engine block, plumbing holes in tanks, stud holes having one closed end and the like. Threads defined in such holes may become damaged during use and if this occurs, repair is often difficult or impossible. Various rethreading and thread repairing tools have heretofore become known to aid in repairing such damaged threads, but none of such prior devices have completely and effectively solved the problem. The instant invention presents a new, novel and improved tool of this class.
Most commonly when threads in a blind hole are damaged, the entire threaded structure is not damaged but rather only a portion. Most commonly the portion that is damaged is that immediately inwardly of the hole orifice as the damage generally is caused by insertion of a threaded element into a hole that is either misaligned upon attempted establishment or has threads of a different nature than those defined in the hole.
A thread reforming or repair tool to be operative must necessarily be aligned with the existing threaded structure and by reason of the position of damaged threads, this generally requires the tool to be established in the threaded structure inwardly of the damaged portion. The tools of the prior art either have not accomplished or have not effectively accomplishied this end.
My tool in contradistinction provides a relatively short, fluted thread forming portion at one end having a relaxed diameter smaller than the internal diameter of the thread to be reformed and with no portion of the tool on either side of the thread forming portion having a larger diameter. With this structure then, the tool may be inserted past damaged threads in a blind hole and there expanded into mating engagement with the good properly formed threads in the hole to establish a mating contact therewith so that upon rotational withdrawal from the hole the damaged threads are repaired and reformed in proper relationship with the original threads inwardly thereof.
The tool disclosed by Sanger in U.S. Pat. No. 4,661,028 is representative of prior devices. The reference teaches the use of a tapering and fluted threaded tap that is expandable by means of a forcing cone threadedly engaged on a rod carried in the medial channel axially defined through the tap. With this device the portion of the threading tap that first contacts the threads of an existing hole must necessarily be the portion adjacent the orifice of the threaded hole, since that is the diametrically largest portion of the rethreading tap. This causes the tap to first contact the damaged threads in a hole, which most probably may misalign the tap relative to the undamaged threads and if so, may further damage the threaded structure possibly to a point where it may not be repairable. It is this problem which the instant invention overcomes.
My invention resides not in this feature per se, but rather in the synergistic combination of all of the structures that necessarily give rise to the functions flowing therefrom as herein specified and claimed.